Hi Henry, some collectors like sequential serial numbers when buying multiple firearms. Some like to match up special dates, number sequences to special occasions. Lots of reasons for different folks. Cheers and stay safe!

the only reason I would is if I was buying more than one for my family then I could look for a block of s/n numbers

Henry, for most people, it makes no difference. Some people like to match a serial number with a specific date, such as birthday, etc.
For collectible guns, you may want the lowest number possible. Or if you buy a gun for yourself and your wife, you may want sequential numbers. I'm sure there are other reasons too, but as I said in the beginning, for most folks, it really doesn't matter.
Stay safe & have a great day!