I do if the box set works out cheaper than buying them individually and I sense I will like them. So for example, I read most of ACOTAR and then saw that the boxset of Throne of Glass series was on Amazon for about 45-50 last year, which worked out about 5-7 per book. At the time I knew I liked the author's writing enough to know it was worth the risk, and a friend was already half way through the series and was enjoying it.
I discovered Strike books about 4-5 years ago., I bought Book 1, LOVED it, bought Books 2-5 in one go at Waterstones with vouchers, and then pre-ordered 6 and 7 when they each came out.
Currently on my TBR are the PD James Dalgliesh books. I read the first and loved it, and splurged on the next 3 books, but there are like 14 in total... and technically I think each can be standalone. I've told myself as there are so many, I must read the other 3 I have got on my pile first before buying more of the series.
For other new-to-me series, I am trying to just buy the first one, but the urge is strong to get them all, ahahah.
I am slowly working my way through Georgette Heyer and Agatha Christie over the past few and future years, as a long-term goal. I have a spreadsheet (because I can never remember all the things on my TBR otherwise), and I have those books on my wishlists so when I see some go on sale, I'll pick them up. Some of the Christies seem to be out of copyright now so there are some cheap copies as ebook available now, depending on the publication year.
I have desperately run out of space for physical books though, so I will either need to cull some to be donated, or seriously be more careful which physical copies I buy. I do love the space-saving nature of ebooks, but sometimes a lady just wants to go to the bookshop and buy books...


It's a struggle.
That was a long blurb noone asked for.