What TSV is
TSV is CSV with tabs instead of commas. Because tabs almost never appear inside a value, quoting is rarely needed and the files are easier to read by eye.
Bioinformatics, log processing, and anyone who has copied a block of cells out of a spreadsheet: the clipboard format is TSV.
What PNG is
A lossless image format. Text and thin lines stay exactly as drawn, which is what a table is made of.
Slides, chat messages, issue trackers, and anywhere a table has to travel as a picture rather than as data.
What changes when you convert TSV to PNG
The tab is unambiguous, so there is no delimiter to guess. This is the most reliable of the delimited formats to read.
The table is drawn from the data onto a canvas rather than captured from the page, so the whole thing comes out however long it is and however much of it is on screen. Column widths are measured from the content, alternating rows are shaded, and the scale is adjustable so a table for a slide or a print layout can be drawn at two or three times the size.
What carries over from TSV to PNG
TSV records 3 things about a table that PNG has no way to hold.
Nothing in PNG records that the first row is a header. It is drawn at the top and looks like one, which is all that is left of the distinction.
TSV can be read one record at a time. PNG has to be complete before it means anything, so the whole table is held in memory while it is written and a file that gets cut off part way through is not partly usable - it is unusable.
PNG is the end of the line for this data. Reading the table back out of it is a separate and much harder problem than writing it, so keep the TSV if you will need the values again.