Need good advice ob how to clear Pokémon Space

It happens to me.
Then one time I realized what are the used of those good IV pokes but never been touched for battle/pristege?
So I make a decision to make some of them as sacrificial lamb and transfer, especially those very common pokes even though they have good IV...
I only kept those rare and usable Pokes...
I also those pokes with 90+ IV...

93%+ level only, and only those that have the best 2 or 3 move sets at max .

Only leaves the Pareto frontiers, generally above 50%. Above 67%/82% only when necessary.

Pareto frontiers here:
Only keeps higher level Pokémon above 50%.
If a same Pokémon has a lower level and it has a higher IV, keep it; if not, simply transfer it.

Massively transfer good poks is a painfull process. You must admit most of your good mons are useless and let them go back to the professor.
The way I see it is there will be seven gens and only 1000 slots. Sooner or later we will be forced to tranfer very good mons. Why not start right away ?

Once you have decided what pokemon you will transfer, as said above, you should use them as sacrificial material. But this is a very long process. Even a very active gym player only manage to kill 20-30 of these pokemons per day. So, clearing 300-400 slots will take a while, considering you will evolve new mons in the meantime.

End note : before transferring "good mons", I would wait the gym rework...

Maybe a simple way to decide what pokemon to keep is to use gamepress rating.
Just keep pokemon rated 8 and above (51 species) and only those whit good IV and good moveset.

No matter what, wait for the gym rework. You never know. One of those "never used it" pokemons may become "king of the gym" overnight.

Besides the obvious "wait for the overhaul" ...
I reduced from 800 down to about 500 a while ago. My rules of thumb, often ignored, are:
1) Keep the ones you actually use for attack and defense. Due. For all others:
2) Keep only one of each kind, selected either for high IV, optimum moveset, or unique moveset.
2a) For highest evolutions, multiple mons might be kept, but never two with the same moveset. This is the bloating factor, so keep it restricted to special cases.
3) Keep legacies in any case even with bad IV, but never two with the same moveset.
4) High IV stock for evolutions might be kept only if the evolved forms are actually useful.
5) Extremely rare Pokemon might be kept, in case they become useful after a movechange. Should be really rare, as in "three months of collection for one evolution".
6) Very special pokemon are kept without regard to any rules: my first starter, the single shiny, Pikachu with hats, 100%ers.

Do you keep a living dex? If you do, the easiest way to clear up space is to NOT do this. Some pokemon will simply never be any good. Pokemon like Fearow or Seaking are insta transfers.

Other than that, I only keep 2, maybe 3 from each family tree (excluding final forms.) For example I keep only 2 Bulbasaurs, 2 Charmanders, and 3 Squirtles (I have over 500 candies.) I hang on to those for possible changes in movesets in the future. If I hatch something with a higher IV, the lower one is replaced.

I also don't hang on to pokemon in hopes of a double candy event.

My personal biggest waste of space is Eevee and the Eeveelutions...I have been hording Eevees for months...I have a couple dozen Vaporeons...I have been hanging on to them just to see what the gym rework brings, but I do hope I can transfer most of them...it will probably clear up 100 spots...

I've just had to do this, I'm a hoarder... So I looked at all my mons (except commons), including IV's, catch date and catch location (in some cases).

• Keep mons > 88% (and good ones with lower ones)
• My earliest good catches, and some from the first 3 months
• Mons caught in special locations
• Legacy movesets
• Any that are rare or special (event hats)
• More than 2-3 per specie I like (with exceptions)

I'm glad there's a limit, otherwise I might have 10,000 mons to sort through.

Key is not keeping mons with the same moveset...

Just keep the highest CP one (for attacking) and maybe a prestiger...or even dump the high CP one and keep the lower CP one (since it can be raised).

Also, get rid of all general prestigers (I used to keep from 400-1000 CP). Stuff like the Raticate army, dump...or even the Parasect Army, dump (CP too low now)...Save a few key ones, but dump the rest...

For those CPs, keep the best general prestigers like Wigglytuff (simply high HP), Furret, Lanturn, Jigglypuff, Shuckle, etc...mostly, I save the high HP ones since they can tank through most things if needed...Shuckle is boss at very very low CPs actually.

I'm a hoarder as well and recently have had to clean out some space to make room for the event. Once the gym rework happens I will clear out the rest. I expect to clear another 200-300 mons out after the rework. Just waiting to see if any mons get buffed or moves get changed along with the gym rework.

I used to transfer anything that wasn't 82%. Now I basically have to transfer anything below 89-91% when I hatch them. How many 84-89% Goldeens or Psyducks do you really need? What about 7 - 90+ Arboks? Yeah maybe not.

Once the gym rework is done a bunch of mons are going in the candy grinder.