4 EVs in a stat = 1 stat point higher AT LEVEL 100. You won't notice any changes right away if you start at low levels, but as the levels get higher, you should notice that stat you've been EV training in is higher than usual. You want to keep track so that you know that you have the EVs in the stat that you plan on having.
EVs are gained EVERY TIME a Pokemon gains experience from battle, so your lv. 53 Toxicroak may have already maxed out its 510 limit on EVs earlier and therefore, couldn't gain anymore.
If you feel comfortable with them in a notebook, then by all means, go for it.