There's different levels of awful when it comes to Sequential Downloading.
1.A piece should be sequentially downloaded, especially if it's being downloaded from only 1 peer or seed at a time. This is a good thing, especially with 4 MB piece sizes...even allows the pieces to be written to drive in 1 big write which is great for SSDs and keeps fragmentation on HDDs to a minimum. This means fast lines can run more torrents at once without crippling their drives and/or cpus. It's a shame Tixati has such terrible performance in this regard:
https://forum.tixati.com/support/1833/
"the allocating files thing in tixati always takes much longer than other programs"
https://forum.tixati.com/support/2520/
"Tixati v2.38 downloading ...couldn't sustain 100 KB/sec under seemingly unhindered conditions!"
2.A torrent can be sequentially downloaded with no harm if there's only 1 peer and 1 or more seeds...and the peer-now-seed sticks around to seed for awhile. All pieces were equally rare in that case. Transmission client does that.
3.Sequential Downloading isn't so kind if there's more than 1 peer:
4.Worse still is streaming a video torrent, which requires extremely high download speed for 1080p or 4k high-framerate.
If/when streaming fails, bad things can happen even to the streamer:
A 1080p video torrent (5 GB size) might need ~20 mbit/sec upload speed from other seeds/peers constantly to the streamer alone.
A single ADSL 2+ connection is lucky to have 1 mbit/sec total upload speed and probably cannot devote it to a single peer on a torrent.
With the old BitTorrent average of 4 upload slots per torrent, even assuming these ADSL 2+ peers/seeds are only running 1 torrent each they're only giving 1/4 mbit/sec to any particular peer.
But if there's more than 4 other peers, they won't even be uploading all the time to the same 4 peers.
So under those conditions, for the streamer to reach 20 mbit/sec download speed there needs to be roughly 80 ADSL 2+ peers/seeds at a minimum!
4 streaming peers at once could "drain dry" the combined upload of 100 ADSL 2+ seeds.
5.There is an even much worse case scenario than this...
A BT client that makes streaming default behavior and has trouble uploading to others that becomes very popular...
...and allows sequential downloading/streaming on multiple torrents at the same time.