I do close it, mostly just so that things add up correctly no matter which file/files I'm sourcing for the particular command/report.

For example; for my own purposes I usually just work with the current year's file, but for my Fediverse instance I build a page summarizing all related expenses I've logged, so I source all files for that. It's late right now in my timezone so I can't remember for sure whether or not closing years affects that but it certainly can't hurt and only takes a couple minutes per year.

Here's the page in question, I'm rather proud of it: https://polymaths.social/financial-transparency/

I try to close out annually in January (I haven't yet gotten around to it this year), removing 2+ year old data, so my ledger has less than 3yr of data in it. I found that ledger (I haven't compared with hledger for performance) starts getting noticeably slower to run toward the end of the year with the volume of transactions in the ledger-file.

I chose the timeframe because it means that all transactions that get closed/archived-off have cleared. It's more awkward to have pending transactions still in flight when trying to close, and I haven't found a satisfactory solution there (I'm sure there's some Proper Accounting Way To Close Books on Pending Transactions, but I've not had that click in my brain)

I also use a wrapper.ledger and transactions.ledger pair of files. The wrapper contains my opening balances, imports the transactions, then does a few balance assertions at the end. The advantage is that I can concatenate all my transaction files for multi-year reporting:

$ cat initial_opening_balance.ledger 20*.ledger transactions.ledger | ledger -f - …

where the initial_opening_balance.ledger is my initial opening balances when I started using ledger, the 20*.ledger files are previously closed years, and the transactions.ledger is the current data.

Very interesting, thank you!