Do you leave run off water in the tray?

Just looking for some advice. I am going to use 5 gal smart pots (fabric) for the last 3 weeks of veg through 60 days of flower. My question is should I leave run off water in the tray or dump it out? I have read conflicting information on this subject with some saying keep it for the plant to use when needed and others saying dump it out.
Any advice is appreciated,
Thanks.

i do but i test every run of...... if it climbs 200-300 ppm past my feed ...then i will drop feed level to accommodate good reading .

I am new also but thru my research ive learned that you can leave it for about 20 minutes or so cause sometimes plant will absorb runoff if needed...ALSO you will need to check the ph and ppm of the run off before dumping it to make sure your ranges are good...hope that helps!!!

Leaving some for a short amount of time while it is absorbed is ok, but too long and you are creating an ideal breeding ground for mould!