Oh, that's a very difficult question. It's hard to explicity answer it. I'll try though.

Okay, let's put it in contrast. Warning: what I'm going to do now is not grammatically correct but I think it might help a bit. So here we go.

Он видит меня - a perfectly fine sentence meaning "he sees me". But what it'd sound like if we put Я in dative there?

Он видит мне. This one sounds weird, but it also changes meaning a bit. Now it sounds like "He sees for me." Why? Because now the dative case gives us a notion that you are the recipient of the seeing action. Like he sees things and then, somehow, give you the things he saw. I know it's very odd, but hey the original sentence is also bizaar


Она помогала мне - A perfectly fine sentence, because you were given help and help is something that can be given, unlike the seeing process, for obvious reasons I hope (Note: don't say дать помощь in Russian. Although I did say that help can be given, but I didn't mean it literally. What matters here is that help is something that can go from one person to another, when seeing cannot.)

Она помогала меня - Now this sounds weird, also a bit funny. Now it sounds like she didn't give you help, but rather like she used you to perform the action of helping and not like "hey, do this for me and you'll help another person", but like "she imposed help on you" and not in the usual way Anyway, this last sentence sounds mostly like nonsense, hard to even describe it.

Hope this helps in any way.

Note: It might be a good practice to learn both a verb and its common object (if any). It can save you a lot of grief in the long run