There’s no single answer to this – it all depends on what it is that you are glugging. You can over-glug pop-ups with certain liquids.
Glugs such as Sticky L-Zero-30T are naturally quite heavy, so with pop-ups I would either give them a little coating of the thicker liquids, or a healthy amount of bait spray.
Sprays are ideal for pumping extra attraction into your hookbait as the thin liquid penetrates right through to the centre.
If you are planning on glugging freebies, there really isn’t any limit! I stick to natural liquids such as Pure Krill Liquid, the more the merrier, as fish love it.
The only other liquid I use is oil, predominantly Hemp Oil, adding only a light glaze to baits. This tends to be enough for it to do its job.