You don't have to use splits, but it is recommended in case you forget your route

Assuming the question is 'can you use just a timer?', then yes you can. You don't actually need splits or a timer shown, at the end of the day they're just for you.

If the question is 'how do I create splits?', then right click on the timer and select 'edit splits'. Should be self-explanatory from there. If it's not, look up a guide on YouTube or something.

for submitting a run, you only need video-proof (either way twitch or youtube etc...), timers are just for yourself. most of the runs get re-timed/corrected by the mods themselves to check for accuracy and accurancy :)

Many people would agree with you, I personally prefer to hide my splits, so I'm less inclined to reset, but I still use them for data reasons. It's completely your choice, however.

No run ever requires a timer. The run can and will be timed afterwards.

For some runs it's really important to know what you're doing but if you want more practice, hiding them and keeping the data like paintophobia is a good idea. It will allow you to see how you went, rather than how you are going. I also really like using the balanced split option in LiveSplit as well as it's essentially your statistical PB. It can really inform you where you're lacking typically.

One option could be to set up all the splits but just compare against nothing. Then you have all the "data" but don't know how the run itself is going