What LaTeX is
A LaTeX table is a tabular environment: a column specification, ampersands between cells and double backslashes at the end of each row.
Academic papers, theses and anything typeset with LaTeX or written in Overleaf.
What PDF is
PDF describes a page: glyphs at coordinates, not rows and columns. A table in a PDF is a visual arrangement, not a data structure.
Reports, invoices, statements and anything sent to be read rather than processed.
What changes when you convert LaTeX to PDF
The tabular body is read, rules are dropped, and escaped characters are unescaped. Text wrapped in textbf or emph is reduced to the text itself.
The table is drawn into a paginated document with the header repeated on every page, so a long table stays readable past page one. Page size, orientation and font size are all adjustable.
What carries over from LaTeX to PDF
LaTeX records 2 things about a table that PDF has no way to hold.
LaTeX can hold a value that is itself a list or an object. PDF has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
Nothing in PDF 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.