You are right, as we know:
While techniques may require a number of hand seals to work, a skilled ninja can use less or even one to perform the same technique.
So if you are a master shinobi, you can use a jutsu without making seals or making just a few seals, instead of 5-10-20. BUT if you are novice, you can't perform jutsu without hand seals. The number of seals or the number of hands indicates the skills of the shinobi. The more skilled someone is, the less effort he needs to put on casting a jutsu.
An example of this is the Water Release: Water Dragon Bullet Technique, which requires a total of 44 hand seals to activate.Tobirama Senju, the Second Hokage, only needed to use one hand seal to complete the technique, a testament to his skill.Although rare, it is possible for a shinobi to be able to do hand seals with just one hand. The only shinobi seen so far capable of this are Haku, Minato Namikaze and Guren.
The seals are VERY important even if you're skilled. It's vital in the Shinobi World since a jutsu can't be performed without hand seals and just few of the jutstu's are casted without hand seals (e.g Rasengan).