Settings - Transfers - General
These options help control the amount of transfers that are running at a given time. It is important to not run more transfers than your internet connection and/or CPU can handle. Excess downloads will be queued and will start as other downloads complete. Excess seeding transfers will be put into a standby-queue and will activate when other seeding transfers have been stopped (either manually or by hitting a pre-set seeding ratio limit.) Both queues are fully re-orderable by dragging and dropping in the main transfers view.
An automatic transfer queue management system can be optionally used by activating one or both of the checkboxes next to "Auto-manage slots". This will rotate your seeds in and out of standby depending on their seed and peer counts, so that your upload bandwidth is optimized toward seeding rare/needed content with greater priority. This feature will also auto-start queued downloads if needed to fully utilize download bandwidth (if the bandwidth throttle is enabled).
Auto Start / Stop Options
The first option will automatically start newly loaded transfers, whether loaded by .torrent file, magnet link, or new seed creation.
The second option will cause the software to remember which transfers were running when the last session was closed, and will re-start them when the next session has started.
You can also set an upload ratio goal for seeding. There are separate settings for regular seeds and seeds that have been newly created locally. Once the goal ratio is reached, the upload will automatically be stopped. You can customize this setting per-transfer by right-clicking a transfer and using the options in the 'Seeding' sub-menu.
These options are provided for advanced users that want to customize minor aspects of how transfers operate.
PEX is a protocol extension that allows peers to exchange addresses of other peers with each other, in order to maximize the visibility between peers in the swarm. It is usually best to leave the PEX mode set to "Send/Receive".
Standard SSDP-based Local Peer Discovery (not shown in old photo above) has been added as an option for transfers. SSDP Local Peer Discovery is used for finding peers on your LAN. This feature defaults to inactive (for top security on unsecured LANs), but can be set so that all transfers are announced, or just a few can be enabled individually via the Options tab for the transfer. The announcement protocol is the same SSDP over multicast protocol used by other clients, and is fully compatible. However, it should be noted that this protocol, while compatible with other clients, uses no encryption and allows anyone else on your LAN to theoretically identify and log any transfers that are being announced.
It is usually recommended to leave the Abandoned Piece Timeout to "Never".