There are, in my opinion, basically two main times to be interested in thread magic (outside of traditional thread items).
(1) You're looking for a focused boost of power against a particular target, usually to give yourself a better chance of defeating them. For example, you're looking to kill the high-Circle leader of a dark cult, and you aren't nearly as high a Circle. If you manage to obtain one of his pattern items and learn its associated Key Knowledge, you can give yourself increased offense (by boosting your talent steps when interacting with him -- Spellcasting, Melee Weapons, etc), or improved defense (Defense Ratings, Durability, etc) to give yourself a better chance of success.
(2) To enhance your "lair" in some way. Our aforementioned cult leader have a Named temple he's using as a base of operations, and has obtained one of its pattern items. When in that Named space, he can make himself tougher or more powerful (the same way you might against an individual person using one of their pattern items), but this benefit applies to anything he is doing within that space. (Any dragon worth its scales will likely have a pattern item or two for its lair, making them even more formidable while in there -- this would be on top of their already impressive magical abilities.)
Two things to remember. (a) A True Pattern is not required to have any pattern items at all. (b) The only "benefit" from having your own pattern item is knowing somebody else doesn't have it to use against you.
Third thing to remember: Outside of very specific circumstances, it is difficult to force a pattern item to be made. (The big one is basically Group True Patterns, which are their own special thing.) The example of a magician's grimoire becoming one of their pattern items is something a lot of people take as a given, when that's not really the case. It might, certainly, but it isn't guaranteed.(although you could probably make a Major one for this purpose, if you haven't made one before)
The thing is, pattern items and thread magic (outside of traditional thread items, and maybe group patterns -- which, again, their own thing) are something that more-or-less must exist based on the way magic works in Earthdawn, but you don't have to deal with them at all if you don't want to. They work best as a story hook, maguffin, or objective in a greater story. Powerful people likely have them, want to control them (for good or ill), and if one associated with a notable True Pattern turns up, many powerful people are likely to be very interested in them.
(There are extreme workings of magic that use pattern items -- Varulus III's assassination was the enabled because the Denairastas had one of his pattern items, for example. And -- as alluded earlier -- if somebody had one or more of Barsaive's pattern items, that might given them some significant degree of power or control over the province.)