Delegating funds is a mechanism that makes your BP used in the same way as when you use it by voting yourself, i.e. you earn the same from curation. The difference is that someone else simply decides who will receive value of your vote.
The funds still belong to you and you can withdraw them from the delegation at any time. Basically, it is also a security mechanism. Let's say you have a lot of BP and you are worried about your account being hacked, which can most often happen when, for example, as a result of user error or security breach, during everyday use of the network the keys leak in some way. Thanks to delegation, you can secure your funds by creating a second account and delegating the entire BP to it and then using this account on a daily basis. Even if someone hacks into this second account, they will have no possibility of withdrawing these funds. On the other hand, for example, the keys to the first account will be safely stored, for example, in a safe and unused, so the possibility of leakage will be practically zero.
Even if you use both accounts on a daily basis, this gives you additional security because the delegation withdrawal lasts 5 days, which means that the funds you delegate in the event of a hack give you an extra 5 days to realize that someone unauthorized has accessed your account and recover your password before someone can do anything with them.
Another benefit for investors is that if their goal was to simply invest in the blurt network but they don't have time for independent curation but also want their funds to work somewhere where they will be used to support content in a way that resonates with them, they can transfer their funds to applications whose assumptions and purpose of operation are clearly defined or to people who think similarly to them. If you don't like the idea of the Appreciator app, you don't have to delegate your BP here. But maybe you have a friend who actively uses the network and you know that he thinks similarly to you and votes for what you do, then you can delegate funds to him.
On the other hand, if you want to support more initiatives and disperse your funds so that they work for many projects and people, you can divide the delegations into any number of accounts and they will work for you everywhere.