if it's not in your personal wallet it's not yours yet, as simple as that, but surprisingly enough there are actually people that really think that their tokens/coins are totally safe in exchanges, if you ask those people why are they so sure and feel safe, most of them will probably just say because they trust the exchange or something like that, seems to me some people forget previous incidents regarding exchanges getting hacked rather quickly, BitGrail hack that during that incident millions of XRB(Rebranded and known as nano now) got removed from their wallet and the cryptopia hack that happened recently and it wasn't even this exchange's first time that experienced an incident like this and then again people trusted this exchange enough to keep their funds on there, why would anyone trust an exchange with all those previous fishy incidents (like the time when they were having something around 1 month or even more for a simple withdarawal action) and such really?
They didn't forget those exchanges hacked in history. It's just that they used exchanges because of various purposes
e.g buy,sell,deposits, withdraw,convert,less hassle trades etc.
There are lots of reasons why people used exchanges. Remember that not all people does have the same purpose of holding coins for long period. They already understand the risks so to minimized that they will stick to those reputable ones. We can't just say to people to stay away from exchanges but instead give them some enlightment about all the associated risks they will faced once they put money on exchange.
For holding purposes for quiet long period, obviously it's basic that people should not used an exchange wallet.