There is no doubt that in an ideal world you would get all your clothes tailored to fit you perfectly, but as bespoke garments come at a price, bespoke clothes are, for most people, restricted to a carefully selected set of items. The reality is that a significant amount of your clothes will be bought off the rack and although you'll do your best to seek out the configuration which most closely resembles your size and body shape, it is hardly ever a perfect fit. The most common problem is probably trousers which are too long and most people would get that changed. Very few people walk around with their trouser legs dragging along the ground. When it comes to blazers and suit jackets, my impression is that people are generally less bothered about the perfect fit. The sleeves are often too long, the body of the jacket may be too long and often it is too loose or too tight around the waist. It is the little things that let down a good outfit and a slightly to loose waist or too long sleeves do not leave a good impression and attracts negative attention. That is why it is so important to have your off the rack clothes altered to get the best possible fit for your body. It will never be the same as bespoke garments but imagine how nice it would be if everyone wore clothes that actually fitted them. This brings me to the main point of this post, the importance of finding an altering service you are satisfied with. By this, I mean that you should be slightly critical when looking for a person to alter your clothes. The quality of the work and the expertise of the workers can vary greatly. A tailor mainly working with women's clothing may not have the necessary experience with gentleman's clothes and vice versa. Shop around a bit, talk to the tailors, talk to people, look for reviews online and the most important thing of all, do not hand over your most precious clothes the first time you try a new service. Make sure you find someone who does the work to your satisfaction. Having a tailor you trust will make it easier to have alterations done also to discuss the result you are after.
Recently I bought a Charles Tyrwhitt boating blazer from their online shop and by following the sizing guidelines, the jacket fitted reasonably well. The only problem was that it was too loose around the waist and I wouldn't have been able to wear it without being very self conscious about it. Needless to say, I had the jacket sown in and, for a very reasonable price, I now have a beautiful blazer I can wear with my head held high.
Having clothes altered is not very expensive and normally you would only need one or two things done. The little money you spend having your clothes fitted is the best money you could ever spend. Few things beat the feeling of wearing perfectly fitting clothes and, at least, it rids you of the discomfort of an ill fitting garment.