Online shopping is one of my hobby. In internet we can easily get lots of online store for clothing, accessories, jewellery, footwear and so on. I like to buy suit online as well as I get lots of discount offer, free shipping service and so on.
I bought two off-the-rack blazers online. I don't wear either of them as much as I'd like to because the fit is a bit off. There's not enough waist-suppression on the first one, and not enough shoulder slack on the second. The blazer I end up using most is ironically one picked up at a thrift store.
If it was a cheap suite (<£200) then yes. But an expensive suit I would certainly want to try it on.
Having said that, you can always take it to a tailors and have it adjusted slightly to get the fit perfect; if you know your measurements, and those of the suit, it shouldn't ever be too far off for a good tailor to fix.