Heating the brew up to a boil

I thought I would ask this question here, instead of in the all-grain forum.

When I do an all grain brew, I usually take the first runnings, and put them on the heat, while the sparge water is in the mash tun. Depending on the quanity, and how fast the sparge water drains, sometimes, it comes to a boil. Yesterday for example, it came up to a boil, and went through the hot break before I added the sparge water to it. I don't add any hops until all the liquid is in the boil pot and it is all up to a boil.

So here's my question. Is it ok to do this?

FWIW on the brew I did yesterday, I hit my numbers both on OG and amount.

If it is just wort boiling, it wont change anything.

That's all it is. I didn't figure it would make much of a difference, since at this point all you are really doing is concentrating the liquid.