I found Block 507570.
There are only 51 transactions in this block but its size is almost maximal, there are 3,964 input adresses with exactly 0.0001 BTC. The sender paid only 10$ for 61,602 Bytes here for example and there are 19 similar transactions in this block. Is this an attemp to waste space of the blockchain?
looking at this particular example, there is many, many multisig tx, one after another. These multisigs require more signatures, and extend the space. Now one can try to be speculative, and say it is spam - as we don't know the real use case. The advantage would be, that you fill the block of "low level fee tx" (see here: https://core.jochen-hoenicke.de/queue/#30d), so that following tx need higher fees, which pays better off for the miner(s).
Another approach for a use case is cold storage. To reduce the risk, I separate the funds of my exchange users in a hot wallet, and a cold wallet. Every now and then the users will want to move funds around, which might create such huge tx. I haven't followed the addresses though.
A third use case could be mixers. Many people would contribute their initial bitcoins, and then mix it between many different addresses, and bring it out again... In an overall tx, with 10$ fee, you could "wash" +170 US$ of current value.
